Lift cranes typically include a car body; ground engaging members elevating the car body off the ground; a rotating bed rotatably connected to the car body such that the rotating bed can swing with respect to the ground engaging members; and a boom pivotally mounted on the rotating bed, with a load hoist line extending there from. For mobile lift cranes, there are different types of moveable ground engaging members, most notably tires for truck mounted cranes, and crawlers. Typically mobile lift cranes include a counterweight to help balance the crane when the crane lifts a load. Typical cranes include a mast and a boom suspension that is used to change the angle of the boom and provide tension forces to offset the forces applied to the boom by the load on the load hoist line so that the boom can behave as a column member with only compressive forces acting through the length of the boom.
A typical crane is designed to be set up in multiple configurations. Each configuration typically has differing components and varying geometry between components in a given configuration. For example, a crane may be designed to be set up with different boom length configurations to optimize the capacity that the crane can handle, using only as long of a boom as is necessary for a particular lift operation that the crane is being set up for.
Since the crane will be used in various locations, it needs to be designed so that it can be transported from one job site to the next. This usually requires that the crane be dismantled into components that are of a size and weight that they can be transported by truck within highway transportation limits. The ease with which the crane can be dismantled and set up has an impact on the total cost of using the crane. Thus, to the extent that fewer man-hours are needed to set up the crane, there is a direct advantage to the crane owner or renter.
Because of the large size of the components, it may be necessary to utilize a separate crane to remove components from the truck and assemble a crane. Due to the time and expense of operating a second crane, systems and methods have been developed to minimize the use of a second crane. For example, it is common for one of the first components to be assembled to a crane to be a live mast. Or, it is possible that a crane be shipped with a live mast attached. Because the live mast is able to swing past the car body, it is possible to use the live mast as a temporary boom for self-assembly of the crane. However, at this stage of assembly, a crane typically does not have a functioning hoist for lifting operations. Instead, a linear actuator, such as a hydraulic cylinder may be attached to the mast for lifting loads. The linear actuator is attached at a top end of the mast in a rotating connection and allowed to hang freely. When the mast is at an angle of less than ninety degrees relative to the rear horizon of the crane, the linear actuator rests on the mast. As the mast rotates forward to an angle of greater than 90 degrees relative to the rear horizon, the linear actuator hangs from the mast at the rotating connection. With the linear actuator hanging down, it may then be used to lift objects, such as unassembled crane components.
Rather than manually assembling the linear actuator for assembly of the crane and then removing the linear actuator after the crane is assembled, the linear actuator is typically stowed on the mast when set-up is complete. Mobile cranes regularly move about construction sites: to orient the crane to a lift; to traverse a site between lift operations; and to maneuver in and around the site. While the crane is in motion, or during operation, it is important for the live mast mounted linear actuator to be restrained so that it does not swing freely, potentially distracting the operator, causing damage to the live mast, causing damage to the linear actuator, or damaging some other crane component.
This is known problem in the industry and there are a number of approaches used to catch, capture, latch, clamp, hook, or otherwise retain the linear actuator. Each approach has been generally successful in reducing the amount of time required for assembly relative to using a separate crane, or removing the linear actuator altogether. Past approaches have included running a strap over the actuator to hold it against the mast, pinning the actuator to the boom, and hooking an end of the linear actuator to the boom.
Historically, in order to stow an actuator, the live mast would need to be positioned at or near its horizontal position for a person to access the actuator. The person accessing the actuator would then attach a strap to hold the actuator in place or insert a pin to fasten the actuator to the live mast.
Moving the live mast back to the horizontal position requires additional time, so newer designs require that the live mast only be slightly less than vertical. However, stowing the actuator with the live mast in a near vertical position introduces other potential problems. For example, if a person needs to manually retain the actuator through a strap or a pin, they will need to be positioned high enough to reach the actuator, which would ether require a separate lift, or a way for a person to climb to the actuator. Both present potential safety issues and take additional time. Attempts to eliminate the need for a person to access the actuator have been largely unsuccessful to date, as they are either complicated, or are unreliable in operation, often requiring a person to guide the actuator.
It would be beneficial to develop a retaining mechanism that would allow crane setup times to be reduced even further, while maintaining the strength and durability needed for retaining a linear actuator on a crane mast.